The present invention relates to incendiary compositions and more particularly to incendiary compositions which are designed for the ignition of ambient combustible materials upon delivery by detonation of an explosive charge.
Incendiary compositions for ignition of combustible materials have both military use in the destruction of property and war material, and civilian application in the starting of backfires for forest fire control, for example. Several types of incendiary compositions of the general type contemplated by the present invention have been used in the past. Such compositions are incorporated in devices in which an explosive charge either carries the incendiary material to its intended place of use or disperses the incendiary material in a more or less random fashion from the point of detonation of the explosive charge. One common type has used a flowing, powdery mixture of metal and oxidizer or pressed pellets of such powders, which are dispersed upon explosion of an explosive charge. Such devices, of course, inherently have an obvious hazard insofar as handling is concerned because materials are spontaneously reactable. Further, they are not totally satisfactory because the powders tend to burn too rapidly and the explosive charge tends to disperse the powders in an erratic manner and over a very short range before burn-out occurs or causes them to detonate upon application of pressure from the explosive charge. Thus, neither uniformity nor extent of distribution is often optimum.
Other types of known compositions make use of solid compositions such as zirconium-misch metal or Thermits. These materials can be cast into a proper form such as the lining of a shell casing which is then filled with the explosive charge. They tend to suffer, however, from handling difficulties due to vacuums and pressures needed for fabrication and also to early burn-out due to their brittleness and complete disintegration upon being subjected to the extremely high pressures inherent in the high explosive detonation. The disintegration of course results in failure to ignite ambient combustible material. Further, most of these materials are subject to quenching by water and other liquids and will not ignite wet materials which would otherwise be combustible, nor are they useable at high altitudes due to need for oxygen.
A particular type of composition which has been used in the past makes use of magnesium powder with a strong oxidizing agent such as polytetrafluoroethylene or salt type oxidizers such as potassium perchlorate. These materials are extremely hazardous to handle from the standpoint that atmospheric moisture will often cause spontaneous ignition. In the case of magnesium and polytetrafluoroethylene, a solvent compounding method is often used as a safety precaution. However, upon removal of the solvent which adds an extra processing step, a danger exists that atmospheric moisture will inherently enter the material even though precautions are taken to lower ambient humidity. It has also been suggested in the past that inert ingredients can be admixed with the incendiary materials and remain as part of the composition to lessen the opportunity for spontaneous discharge. In the past, however, these expedients have generally caused a reduction in the effectiveness of the incendiary nature of the composition and have not been entirely satisfactory. Furthermore, these materials also are often completely disintegrated or will themselves be detonated by the high explosive detonation.
It has in the past been suggested that silicone materials can be used in flare compositions as a binder. Generally the maximum amount of binder used was in the range of 4-5 percent by weight of the composition, because it was felt that binder merely held the active ingredients together and detracted from the brilliance of the composition. Since no detonation was involved resistance to detonation in the binder material was necessary only to the extent that the material should not detonate upon burning at close to atmospheric pressure. These same flare compositions would detonate if subjected to the pressures of a high explosive charge detonation inside a casing in which they were contained. It has also been found that silicone rubber compositions including magnesium and salt type oxidizers such as potassium perchlorate are subject to detonation.